check.tpo should tell users that only their browser is configured to use Tor
Right now, when accessed through Tor, check.torproject.org tells users “Congratulations. You are using Tor.”. This message really means that the browser that is displaying the message is using Tor; it does not mean that other programs on the user's computer are using Tor.
It would be more correct to tell users “Congratulations. This browser is configured to use Tor.”.